1. Field of the Invention
The present invention relates to an endoscope system for increasing a cleaning power in internal conduits of the endoscope.
2. Description of the Related Art
A cleaning solution such as tap water is generally supplied to clean the internal conduits of an endoscope. To clean paths in the conduits with the cleaning solution flowing through the conduits, the cleaning solution must be hydrodynamically flowed at a flow speed to form a turbulence in the conduit. As a matter of course, the higher the flow speed of the cleaning solution becomes, the better the cleaning effect is, and the shorter the cleaning time becomes. When the flow speed of the cleaning solution is lower than a predetermined speed, the cleaning effect is lost. The flow speed herein is defined as a flow speed V obtained by dividing a flow rate Q per unit time by a sectional area A of the conduit, i.e., V=Q/A.
As described above, the cleaning capability in the internal conduits of an endoscope is regarded to depend on the flow speed of the cleaning solution. The cleaning capability also changes depending on the cleaning power of the cleaning solution itself and the temperature of the cleaning solution. When cleaning is performed using a cleaning solution containing a strong detergent and a high-temperature cleaning solution, contamination caused by an endoscopic examination can be removed. The strong detergent, however, adversely affects the materials of members in the endoscope and may damage the endoscope itself. When the temperature of the cleaning solution is increased, the endoscope itself is damaged. In field applications, tap water is often used to clean endoscopes in a lot of medical facilities. In this case, satisfactory cleaning cannot be achieved by simply supplying a cleaning solution to a conduit.
As described above, to satisfactorily clean the conduits of an endoscope, the cleaning solution must be flowed at a high flow speed and must be hydrodynamically caused to form a turbulence in the conduit.
A turbulence is caused by Reynolds number Re=2,320. A relation between the Reynolds number Re and a flow speed .mu. of a cleaning solution is represented as follows: EQU Re=.mu..multidot.d/.nu.
where d is the inner diameter of the conduit, .nu. is the kinematic viscosity coefficient, and .mu. is the flow speed of the cleaning solution, i.e., the value obtained by dividing the flow rate Q per unit time in the conduit by the sectional area A of the conduit, i.e., .mu.=Q/A (cm/s).
In a channel (conduit) having an inner diameter of 2.0 mm, for example, a turbulence is formed at 116.4 cm/s according to .mu.=Re.multidot..nu./d. The kinematic viscosity coefficient .nu. is 1.0038.times.10.sup.-6 m.sup.2 /s at 20.degree. C. in water. FIG. 1 shows the distribution of velocity vectors v of a cleaning solution b when the cleaning solution b is flowed in a conduit a of an endoscope. As is apparent from FIG. 1, the flow speed is high at the center of the conduit a and decreases near the inner wall surface of the conduit a. It is thus assumed that a turbulence is not formed at the wall surface at Re.div.2320.
An experiment was actually conducted to measure a flow speed required for cleaning the inner wall surface of a conduit. In this case, filth containing a protein, which is assumed as a body fluid, was injected in a Teflon channel tube having an inner diameter of 2.0 mm, and tap water was supplied to the tube to clean the interior of the tube. FIG. 2 shows the result in a graph representing a relationship between the cleaning time and the flow speed of the cleaning solution.
As can be apparent from FIG. 2, the cleaning power abruptly increases at a flow speed .mu.=170 cm/s or more in the channel having the inner diameter of 2.0 mm. In this case, the Reynolds number is Re=3,387. The conduits of an endoscope must be cleaned at Re=3,387 or more.
The internal conduits in a general endoscope are classified into an air supply conduit, a water supply conduit, a treatment tool insertion conduit, and a suction conduit. To clean the conduits, a cleaning solution is supplied, using a solution supply pump, from the cylinder of a conduit switching valve from which a piston is removed. The maximum inner diameters of the conduits in endoscopes are given as follows. That is, the inner diameter of an insertion-section-side air supply conduit is 1.5 mm, the inner diameter of the water supply conduit is 1.5 mm, the inner diameter of the suction conduit is 5.5 mm, the inner diameter of the universal-cord-side air supply conduit is 2 mm, the inner diameter of the water supply conduit is 2.4 mm, and the inner diameter of the suction conduit is 4 mm.
To clean all these conduits at a flow speed corresponding to Re=3,387 or more, the necessary flow rate Q of the cleaning solution, i.e., Q=.mu..multidot.A=Re.nu./d.times..pi.d.sup.2 =Re.multidot..nu..multidot..pi..multidot.d/4 from .mu.=Q/A' and .mu.=Re.nu./d. For this reason, on the insertion section side, the flow rates Q required to clean the above conduits are 14.69 ml/sec for the suction conduit, 4.01 ml/sec for the air supply conduit, and 4.01 ml/sec for the water supply conduit. On the universal cord side, the flow rates Q required to clean the above conduits are 10.68 ml/sec for the suction conduit, 5.34 ml/sec for the air supply conduit, and 6.41 ml/sec for the water supply conduit. A total flow rate is 45.14 ml/sec=2708 ml/min. That is, a flow rate of about 3 l/min is required to clean all the internal conduits of the endoscope. When a cleaning solution has this flow rate (about 3 l/min), a flow speed corresponding to Re=3,387 or more can be obtained.
In the prior art, however, a pump for discharging a cleaning solution to these conduits at the above flow rate is not almost taken into consideration. That is, to clean an endoscope having internal conduits, the endoscope is placed in a cleaning tank. A cleaning solution is sprayed from a nozzle arranged in the cleaning tank to the outer surface of the endoscope, and at the same time the cleaning solution is supplied to the internal conduits of the endoscope, thereby cleaning the exterior and interior of the endoscope. In this case, a pump for supplying the cleaning solution to the internal conduits of the endoscope and a pump for supplying the cleaning solution sprayed on the outer surface of the endoscope are normally constituted by a single pump, as is described in Published Unexamined Japanese Utility Model Application No. 64-26005. In this prior art application, although a pump delivery pressure is defined, the flow rate of the cleaning solution is not defined.
In addition to a cleaning scheme for supplying a cleaning solution such as tap water or a detergent in conduits to clean the conduits of the endoscope, a cleaning scheme for supplying a fluid mixture of a cleaning solution and a gas, i.e., a so-called two-phase (gaseous and liquid phases) flow is also known as a scheme for cleaning the conduits in the endoscope. In this two-phase flow cleaning scheme, an exact amount of cleaning solution actually supplied to the conduits of the endoscope to be cleaned cannot be known because the gas supplied from the air supply pump is mixed with the cleaning solution before the cleaning solution is supplied to the conduits.
An endoscope cleaning system having a cleaning pump for cleaning internal conduits can supply a cleaning solution to the conduits of the endoscope. However, the flow rates for the respective conduits are not defined, and a criterion for satisfactorily cleaning the conduit is not clear. A pump having a capability regarded to be appropriate in accordance with the size of a cleaning apparatus and its layout is selected.
Even if a cleaning solution flows at a flow rate for generating a flow speed corresponding to Re=3,387 or more, a recessed portion 202 is present at a joint between conduits 200 and 201 from the microscopic viewpoint, as shown in FIG. 3. The cleaning solution (arrows in FIG. 3 indicate the flow direction of the cleaning solution) tends not to be brought into contact with the inner surface of the conduit at the recessed portion 202. In addition, the cleaning solution stagnates inside the recessed portion 202. It is therefore difficult to obtain a desired flow speed (i.e., a flow speed corresponding to Re=3,387 or more) for satisfactory cleaning.
The internal conduits of the endoscope include a branch point at which one conduit branches into a plurality of conduits and a merging point at which a plurality of conduits merge into one conduit. The branch and merging points are formed by simply connecting conduits having different inner diameters. Flowability of the cleaning solution in the conduits is not taken into consideration upon conduit connection. For example, the inner diameters of the conduits merging at a merging point may be equal to each other, or the inner diameter of an upstream conduit from which a cleaning solution is injected may be much larger than the inner diameter of a downstream conduit.
When the cleaning solution is caused to flow to such a branch point, and conduits merging at this merging point have almost equal inner diameters, the flow speed of the cleaning solution flowing in the downstream conduit decreases by the number of conduits branching on the downstream side. The flow speed in each downstream conduit is much lower than that in the upstream conduit.
When the diameter of an upstream conduit from which a cleaning solution is injected is much larger than that of a downstream conduit, the flow resistance in the downstream conduit is high, and the cleaning solution cannot smoothly flow in the downstream conduit. As a result, the flow speed of the cleaning solution in the upstream conduit also decreases.
In either case, the cleaning powers within the conduits vary, and the conduits cannot be cleaned with a good balance. In other words, even if a cleaning solution is flowed sufficiently, some conduits cannot be satisfactorily cleaned, or the cleaning solution must often be kept flowed to the cleaned conduit so as to clean a conduit in which the flow speed of the cleaning solution is low, thereby wasting the cleaning solution.
When the inner wall surface of a conduit is a rough surface as in a stainless steel pipe, the conduit resistance increases to lower the flow speed of the cleaning solution near the wall surface of the pipe. In the stainless steel pipe, the inner wall surface has a relatively sharp crack-like groove. When such a surface is to be cleaned, it is difficult to bring the cleaning solution into contact with the entire surface, and the cleaning power is low.
In a bent portion of an internal conduit in an endoscope, the flow speed of a cleaning solution flowing on the outer side of the bent portion generally tends to be higher than that flowing on the inner side thereof. Therefore, the cleaning power on the outer side of the bent portion is high, while the cleaning power on the inner side of the bent portion is low.
In consideration of the cleaning powers in the internal conduits of the endoscope, the flow speed and flow rate of the cleaning solution and the conduit structure of the internal conduit are important parameters. In the prior art, almost no consideration has been given to the flow speed and flow rate of the cleaning solution and the conduit structure to clean the internal conduits.